This is a proposal for the continued study of human eye movement responses to earth horizontal axis rotations. Comparisons will be made with analogous earth vertical axis rotations in order to characterize the response due to subject rotation with respect to gravity,k the putative otolith ocular reflex. Follow up studies in yaw axis, which employ different stimulus conditions, are proposed based upon results of the previous grant period. In addition, newer yaw axis studies will concentrate upon optokinetic nystagmus and afternystagmus and upon the alteration of the otolith ocular reflex using short term canal ocular adaptive experiments. These studies have not been performed elsewhere in humans. The development of pitch axis protocols and acquisition of a normative data base uniformly distributed by age (20 - 79 years) and equally distributed by gender will be undertaken using a newly installed, two channel, magnetic search coil system to measure vertical eye and head movements individually. Selected patients having unilateral peripheral vestibular lesions or cerebellar deficits will be tested in collaboration with an otologist and a neurologist.